Why Understanding Space Is So Hard • Hacker News Board

Re: Why Understanding Space Is So Hard

#31

Post by pdonis » Wed, Jan 27, 2016, 6:57 PM UTC

colordrops wrote: post #26

Spinning motion is an illusion and doesn't exist as a fundamental form of movement, similar to how lack of gravity in orbit is an illusion, in that you are continuously falling downward but missing the earth. Spinning objects are made of particles that are all actually going in straight lines but forces against each other are causing them to change direction, cummulatively appearing to be spinning, like an extremely…

> Spinning motion is an illusion and doesn't exist as a fundamental form of movement

If there is no objective space, then "movement" in general is not a fundamental concept; but you are assuming that at least some kinds of movement are fundamental (tarikjn points out something similar to this).

> similar to how lack of gravity in orbit is an illusion, in that you are continuously falling downward but missing the earth.

Actually, you have this backwards; it's the "falling downward" because of "gravity" that is the "illusion", according to our best current theory, general relativity. In a free-fall orbit, you are moving in a straight line through spacetime; you can tell this by the fact that you are weightless.

Re: Why Understanding Space Is So Hard

#32

Post by jerf » Wed, Jan 27, 2016, 6:58 PM UTC

colordrops wrote: post #26

Spinning motion is an illusion and doesn't exist as a fundamental form of movement, similar to how lack of gravity in orbit is an illusion, in that you are continuously falling downward but missing the earth. Spinning objects are made of particles that are all actually going in straight lines but forces against each other are causing them to change direction, cummulatively appearing to be spinning, like an extremely…

Physicists are rather aware of these things, seeing as you they are the ones who taught them to you in the first place. This is an old, venerable question that, as the article says, dates back to before Einsteinian relativity and remain unresolved to this day. Physics 101 is not capable of resolving the matter.

Re: Why Understanding Space Is So Hard

#33

Post by pdonis » Wed, Jan 27, 2016, 6:59 PM UTC

kazinator wrote: post #24

The question "would space still exist if matter disappeared" is posed with an ontological bias which influences the answer. A better question is: does a universe in which there is nothing (and never has been) still contain space? (Though a better question, I wrecked it by introducing "never", which presupposes that the universe has time---even though it contains nothing, and therefore no events take place.) The quest…

> does a universe in which there is nothing (and never has been) still contain space?

Within the framework of our best current theories, the answer is yes, in the sense that flat Minkowski spacetime, containing no matter or energy anywhere, is a valid solution of the Einstein Field Equation of general relativity.

Re: Why Understanding Space Is So Hard

#34

Post by colordrops » Wed, Jan 27, 2016, 7:03 PM UTC

pdonis wrote: post #31

colordrops wrote: post #26

Spinning motion is an illusion and doesn't exist as a fundamental form of movement, similar to how lack of gravity in orbit is an illusion, in that you are continuously falling downward but missing the earth. Spinning objects are made of particles that are all actually going in straight lines but forces against each other are causing them to change direction, cummulatively appearing to be spinning, like an extremely…

> Spinning motion is an illusion and doesn't exist as a fundamental form of movement If there is no objective space, then "movement" in general is not a fundamental concept; but you are assuming that at least some kinds of movement are fundamental (tarikjn points out something similar to this). > similar to how lack of gravity in orbit is an illusion, in that you are continuously falling downward but missing the eart…

Regarding gravity, that was probably a bad analogy. Regarding movement, movement relative to other objects is fundamental. You are begging the question by assuming objective space is required for movement.

Mind you, I'm not arguing that space doesn't exist, only that Newton's argument is flawed.

Re: Why Understanding Space Is So Hard

#35

Post by [deleted] » Wed, Jan 27, 2016, 7:05 PM UTC

tarikjn wrote: post #29

colordrops wrote: post #26

Spinning motion is an illusion and doesn't exist as a fundamental form of movement, similar to how lack of gravity in orbit is an illusion, in that you are continuously falling downward but missing the earth. Spinning objects are made of particles that are all actually going in straight lines but forces against each other are causing them to change direction, cummulatively appearing to be spinning, like an extremely…

Suppose your object is the only thing in space, how do you tell that it is spinning? How do the particles in the object can tell that the object as a whole is spinning? What you describe are particules going in straight lines, but over what space/grid are they going on a straight lines? If they are going over straight lines on something then your description is one of an objective space. If pulling forces are still e…

[deleted]

Re: Why Understanding Space Is So Hard

#36

Post by ratsmack » Wed, Jan 27, 2016, 7:06 PM UTC

kazinator wrote: post #24

The question "would space still exist if matter disappeared" is posed with an ontological bias which influences the answer. A better question is: does a universe in which there is nothing (and never has been) still contain space? (Though a better question, I wrecked it by introducing "never", which presupposes that the universe has time---even though it contains nothing, and therefore no events take place.) The quest…

Time is simply a measure of change, so if there is nothing to change how can there be time?

Re: Why Understanding Space Is So Hard

#37

Post by givan » Wed, Jan 27, 2016, 7:22 PM UTC

kazinator wrote: post #24

The question "would space still exist if matter disappeared" is posed with an ontological bias which influences the answer. A better question is: does a universe in which there is nothing (and never has been) still contain space? (Though a better question, I wrecked it by introducing "never", which presupposes that the universe has time---even though it contains nothing, and therefore no events take place.) The quest…

Nothing is an abstract concept that we use for various things, when we say nothing is just a way of saying the absence of something we know, our own existence (Descartes) is proof that absolute nothingness is not possible.

Re: Why Understanding Space Is So Hard

#38

Post by pdonis » Wed, Jan 27, 2016, 7:27 PM UTC

colordrops wrote: post #34

pdonis wrote: post #31

Earlier quoted context omitted.

> Spinning motion is an illusion and doesn't exist as a fundamental form of movement If there is no objective space, then "movement" in general is not a fundamental concept; but you are assuming that at least some kinds of movement are fundamental (tarikjn points out something similar to this). > similar to how lack of gravity in orbit is an illusion, in that you are continuously falling downward but missing the eart…

Regarding gravity, that was probably a bad analogy. Regarding movement, movement relative to other objects is fundamental. You are begging the question by assuming objective space is required for movement. Mind you, I'm not arguing that space doesn't exist, only that Newton's argument is flawed.

> movement relative to other objects is fundamental

I agree that "objective space" in the sense of "a space that is the same for everyone", is not required to give an account of movement of objects relative to other objects. However, the only reason we know that is that we have an alternative: a theory of objective spacetime that gives an account of movement of objects relative to other objects.

In other words, according to our best current classical theory, general relativity, Newton's argument was flawed not because nothing objective is needed to account for the bucket experiment, but because he got wrong what thing was objective: he thought it was space, but it's actually spacetime. More precisely, it's the geometry of spacetime.

On the GR viewpoint, we can indeed view the rotation of Earth, for example, as relative in this sense: we can adopt a "cosmic" frame in which the Earth is spinning and the rest of the universe is at rest; or we can adopt a "geocentric" frame in which the Earth is at rest and the rest of the universe is spinning. Both frames are valid; neither one is "preferred" by the laws of physics. But both frames are describing the same underlying objective thing: the same geometry of spacetime. They are just describing it from different viewpoints.

Re: Why Understanding Space Is So Hard

#39

Post by evanpw » Wed, Jan 27, 2016, 7:41 PM UTC

DubiousPusher wrote: post #25

aardvark179 wrote: post #12

Earlier quoted context omitted.

Consider the outside of a straw. The surface is a curved two-dimensional space which is bounded in one direction only by the length of the straw, but is quite small in the other (the circumference of the straw). If the straw is very long and very thin then it may appear to be essentially 1-dimensional, but the surface is still two dimensional.

Nice example. Wouldn't there be easily measurable evidence of this? Imagine a flattened caterpillar like creature living on such a straw. Unwittingly, one day it might wrap itself round the straw many times. Looking back, seeing itself turned round the straw in this way, wouldn't it see slices of itself rather than a whole?

In the caterpillar's universe, light rays wrap around the surface of the straw too, so they won't see anything "missing".

Re: Why Understanding Space Is So Hard

#40

Post by DubiousPusher » Wed, Jan 27, 2016, 7:48 PM UTC

evanpw wrote: post #39

DubiousPusher wrote: post #25

Earlier quoted context omitted.

Nice example. Wouldn't there be easily measurable evidence of this? Imagine a flattened caterpillar like creature living on such a straw. Unwittingly, one day it might wrap itself round the straw many times. Looking back, seeing itself turned round the straw in this way, wouldn't it see slices of itself rather than a whole?

In the caterpillar's universe, light rays wrap around the surface of the straw too, so they won't see anything "missing".

Awww, of course.